The invention relates to a pneumatically operated interlock device adapted for use with a pressure medium actuator of the axial-piston type.
German patent DE 3,233,940 C1 discloses a quick-clamping device for the clamping of tools or workpieces, having a displaceable locking slide and a slide like adjusting element coupled thereto by means of two tappets. The two tappets act in the same direction on the locking slide, their adjusting strokes being added together, that is to say, within the meaning of the present invention, they actuate the locking slide in the direction of the interlock position. The locking slide is fixed to a dual action clamping piston of the axial-piston type, which is aligned with it and which can be subjected simultaneously to the same working-pressure medium in relation to the axial piston actuating the adjusting element. The total stroke of the two tappets is used to actuate the locking slide over its relatively large idling stroke, so that a small stroke and high working pressures can be provided for the actual clamping operation, whereas a low working pressure is considered sufficient for the idling stroke. In this known quick-clamping device, the locking slide cannot be retained mechanically (that is, without the force of a pressure medium) in the end positions of the axial piston actuating the adjusting element, by actuation of the tappets beyond the dead center position, because the adjusting element is arranged movably along the axis of the housing bore receiving the locking slide, as a result of the stroke of its clamping piston, must have in relation to the housing a greater axial movability which cannot be canceled by the total stroke of the tappets.
German patent DE 3,434,054 A1 discloses a positional interlock device for drive shafts, in which the drive shaft has a toothed rim, into the tooth spaces of which a locking bar can be pushed radially. Engaging with the locking bar is an eccentric drive, the eccentric pin of which is clamped between two sliding bodies movable in the radial direction within the locking bar. The two sliding bodies are biased in the direction of the eccentric pin. Fixed sensors interact with parts of the locking bar, in order to switch off the eccentric drive when the dead center position is exceeded by a predetermined angle, at which the locking bar is held with a self-locking effect by mean of the force of the springs, without the need for force to be exerted by the eccentric drive.
In another known interlock device (German Patent Specification 3,427,160), the engagement member of the locking element consists of a rack profile which, in the interlock position, engages into a mating rack profile on the piston rod of a pressure-medium actuator of the axial-piston type working as a hydrostatic steering motor of an additional steering of a motor vehicle. For this purpose, the working cylinder of the steering motor has a lateral orifice, into which the housing of the interlock device is inserted from outside.
The object of the present invention is to provide a compact actuating means for a locking element with an interlock position and a free position, which facilitate effective retention of the two end positions.
This object is achieved by means of an interlock device according to the invention, in which the additional tappet actuates the locking slide into its free position, as does the other tappet, by passing through a dead center position, whilst at the same time compressing an elastic cushion, thus ensuring a retention of the two end positions without the action of an auxiliary pressure-medium force.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.